Field of the Invention
The invention relates to agricultural equipment, and more particularly to a sieve apparatus for use in combines.
Reference to Prior Art
Most grain and seed crops ("grain") are harvested by first roughly detaching the grain from unwanted portions of the source plants and incidental matter such as rocks and weeds by means which are carried in the forward end portions of harvesting combines. A mixture of detached grain and other vegetation parts ("chaff") is carried by conveying means into the interior of the housing of the combine for processing to further separate and recover the grain from the chaff. In the course of processing within the combine, the mixed grain and chaff are passed over agitated sieves which are adapted to permit the grain to fall by gravity therethrough for separation from the larger chaff.
Conventional sieve assemblies include a generally rectangular frame and a plurality of overlapping banks of slats which define sieve openings through which the grain falls by gravity. Each bank of slats typically includes two or more slats separated by a divider(s) and mounted end-to-end on a metal wire rotatably mounted between the side members of the frame, and a sieve assembly typically includes eight or more such overlapping banks of slats in a single rectangular frame. In some cases, a single slat and no divider can be used. The frame typically also includes one or more elongated dividers extending parallel to the side members and including a plurality of longitudinally spaced apertures rotatably supporting the wires intermediate the frame side members. Sieve assemblies are typically assembled by sliding the wires through the respective apertures in each divider, so that the dividers are "strung" on the wires before the ends of the wires are inserted into the frame side members. In some cases, the side members and dividers are split, can be two halves and can be disassembled to remove wires.
The sieve assembly typically also includes an elongated adjustment bar which extends perpendicularly to the metal wires and includes a plurality of longitudinally spaced recesses or apertures for engaging a crank on each wire and thereby controlling the angular disposition of the slats and the size of the openings between the banks of slats. By this arrangement, the slats can be adjusted to any position between fully open and fully closed. The sieve assembly is supported for reciprocal shifting movement or agitation to cause the grain to separate from the chaff and fall downwardly through the openings between the banks of slats.
The slats usually are made from sheet metal and are rigidly secured to the wires by spot welding, soldering or the like. The wire and welds or solder are exposed to material passing between adjacent slots and some materials can become snagged between a slat and the wire, particularly crops or weeds which are bearded and/or have fine stems.
James et al. U.S. Pat. No. 3,334,744 discloses the use of plastic slats including outwardly projecting journals on the opposite ends through which the wire extends. The journals are received for pivotal movement in recesses in the frame dividers and prevent contact and wear between the wires and dividers. Each slat also includes a longitudinally extending tie-gripping portion on the lower surface for receiving the wire. Each wire includes a major portion and a plurality of radially offset portions corresponding to a tie-gripping portion on each slat. Each tie-gripping portion has a longitudinally extending passage for receiving the major portion of the wire and a radially outwardly extending slot for receiving the offset portion. The slot is tapered, with the narrowest part having a width less than the diameter of the wire. The slot and passage are otherwise dimensioned so that, to mount a slat onto a wire prior to assembly of the dividers and frame side members, the major portion of the wire can be pressed through the slot and snapped into place in the passage, and the offset portion is disposed in the slot to thereby retain the slat for common rotation with the wire.
With such an arrangement, the slats must be installed on the wire prior to completing assembly of the side frame member. Also, in the event a slat breaks during use and must be replaced, the side frame member must be disassembled to permit withdrawal of the slat journals. Furthermore, the tie-gripping portions do not positively lock the slat onto the wire. Consequently, if a pulling force is applied on a slat in a direction diametrically opposite to the slot, the slat can be accidentally pulled off the major portion of the wire. When this occurs, the slat is inoperative, because the wire is free to rotate relative thereto. Such a force can be applied when an operator uses a rake or other tool to remove debris, mud, snow, etc. from the sieve assembly.